Patent GB-191329426-A (GB)
Title: Improved Circuit Arrangements for Automatic or Semi-automatic Telephone Systems.
Filed: 1913-12-20
Granted: 1915-07-22
Abstract: 29,426. Siemens & Halske Akt.-Ges. Dec. 20, 1912, [Convention date]. Automatic and semi-automatic exchange systems.- Relates to private branch exchange and other systems in which certain subscribers are unable to obtain connexions through the main exchange. The invention is applicable to full automatic working in which exchange calls are made through a certain level of a rotary connector, local calls being made on other levels, and also to semi-automatic systems in which the operator, who sets up the call, does not know whether the subscriber wanting an exchange connexion is entitled to it or not. First arrangement, Fig. 1. In the three-wire system shown in Fig. 1, the entitled and non- entitled sub-stations have different constructions of impulse-sender, that of the non-entitled station being designed to send two impulses over the b-line after the transmission of the selecting-impulses over the a-lead. When an entitled subscriber wishes to make an exchange call, he raises the wipers of the rotary connector to the exchange level, thereby closing the contacts k<1>, k<2>, k<3>, and the control impulse over the b-line moves the side switch into its second position and energizes a selflocking relay F, thus completing the circuit of the magnet D, which rotates the connector until an idle exchange line is found. If a non-entitled subscriber tries to establish an exchange call, the second control impulse over the b-line energizes a self-locking relay G, which (1) opens the speaking leads at contacts 9, 10, (2) transmits a busy signal to the subscriber, and (3) opens the circuit of the magnet D at contact 15 so as to prevent the rotation of the connector, or alternatively opens the test lead of the exchange line. Second arrangement, Fig. 2. In the system shown in Fig. 2, all the subscribers have the same form of impulse-sender, but the bank terminals of the preliminary selectors VW of non-entitled subscribers t are connected to the connector trunk through a relay R, normally short-circuited by a switch contact k<4>. When a non-entitled subscriber raises the connector to the exchange level, the relay R is energized, and opens the connexion at contacts 12, 13. Third arrangement, Fig. 3. In the three-wire system shown in Fig. 3, in which the selecting- impulses are transmitted by interrupting the a-lead, while earth is permanently connected to the b-lead, the entitled subscribers have impulsesenders of the usual construction, but the impulsesenders of the non-entitled subscribers are designed momentarily to interrupt the b-lead just before earth is cut off from both leads. To make an exchange call, an entitled subscriber raises the wipers to the exchange level by the vertical magnet H, thereby closing the contacts 25, 26, and when the impulses cease, the relay X opens the circuit of the magnet S, moving the side-switch into its second position. The subscriber again sends in impulses, which are repeated to the rotary magnet D, thus rotating the connector until an idle exchange line is reached, whereupon the test relay P disconnects the rotary magnet. If a non-entitled subscriber tries to make an exchange call, the interruption of the b-lead after the first set of impulses energizes a self-locking relay F, which interrupts the speaking leads and connects a buzzer Su to the calling line. In a modification, the relay F may short-circuit the test relay P. Fourth arrangement, Fig. 5. In cases in which there are only a small number of exchange lines, instead of providing special relays &c. at each selector for preventing the speaking connexion, the special relay may be associated with the exchange line. The subscriber's impulse-senders are constructed as described in connexion with Fig. 3. After the connector has been raised to the exchange level by a non-entitled subscriber, and rotated to find an idle exchange line as described in connexion with Fig. 3, the momentary interruption of the b-lead closes contact 42, thus directly grounding the test-lead c and energizing the relay C, which interrupts the speaking lead. The relay C does not energize when in series with the relay P, so that it is not affected when an exchange call is made by an entitled subscriber. Semi-automatic working. Fig. 6 shows the invention applied to a eemi-automatic system in which the operator, who sets up the call, does not know whether the station wanting the exchange connexion is entitled to it. The bihk terminals of the preliminary selectors VW of stations T entitled to exchange connexions have a relay R arranged in the selector trunk. When a subscriber calls, he is connected by his preliminary selector VW or VW<1> and a service selector DW to an operator's position. After the operator has enquired the wanted number, and before she sends out the selecting-impulses, the contact II is closed, thus energizing a relay T<2> controlling the speaking connexion. A holding-circuit for this relay is closed over the test-wire of the group-selector IGW unless opened at contact 56 by the relay R, so that speaking connexions can only be obtained by subscribers having access to the selector through a relay R.